Soil Carbon Balance in the Coastal Plain Loblolly Pine Plantations.

The stability of soil organic matter has been recognized as a key factor determining the biosphere-climate feedback of the CO₂-mediated increase in land surface temperature. Several recent studies have reported consistent loss of C from various soil types over recent decades. The most vulnerable ones, as well as the most significant ones from climate change perspective are soils with large C stocks. In current study, we evaluate heterotrophic soil respiration (Rh) in the context of total ecosystem carbon balance in the carbon-rich soils in coastal North Carolina. We found that Rh consistently exceeded new litter inputs to the soil, and that the imbalance was greatest during an unusually wet year. Furthermore, the litterfall:Rh ratio was highest, but still smaller than 1 during the most productive year, suggesting that through most of the rotation cycle, soil C stocks are not replenished by new inputs in this pine plantation. If the study period is representative of long-term patterns, the average annual loss of 109 g C m^-2 is nearly double of the average loss of soil C reported for all nonpermafrost peatlands in the conterminous US.